A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The substrate is held by a substrate table, which is moved by an actuator so as to be able to irradiate consecutive parts of the surface of the substrate, e.g. using a stepping or scanning procedure. In a common implementation, the actuator comprises two main parts: a lower part (the so called long stroke) which is responsible for the coarse positioning and an upper part (the so called short stroke) which is responsible for the fine positioning. In order to optimize the performance of the short stroke, as little as possible disturbances shall act on the short stroke. This means that ideally no mechanical or other coupling exists between the long stroke and the short stroke, such that long stroke movements or deformations do not negatively impact the short stroke performance. Conventional designs have minimized the crosstalk by using a minimized number of very flexible connections, and actuation by a 6 degrees of freedom (DoF) Lorentz actuator system.